This invention relates to a hydraulic media for hydraulic processes and apparatus. More particularly, the invention relates to a hydraulic media comprising a microgel dispersion. The microgel dispersion is a Non-Newtonian fluid. This microgel dispersion is useful in devices that utilize a hydraulic fluid, such as hydraulic energy transmission systems and mechanical energy absorbing devices. Examples include hydraulic brake systems, liquid springs, and dynamic damping devices such as aircraft landing gear shock struts, car bumpers, and automobile shock absorbers. Methods of transmitting hydraulic energy and for dissipating kinetic energy using this microgel dispersion are also disclosed.
Hydraulic devices employ a fluid as the working medium, and many prior art devices employ organic fluids. In many applications, silicone fluids have replaced organic fluids because silicone fluids are more chemically stable, they can be employed at higher operating temperatures, and the viscosity of certain silicone fluids is less dependent upon temperature changes than prior organic fluids. A silicone hydraulic fluid having improved viscosity stability with respect to temperature is described in U.S. Pat. No. 2,398,187. Prior art hydraulic fluids tend to be difficult to seal, especially at higher pressures greater than 5000 psi.
Elastomers having the ability to flow like a liquid have been employed as energy dissipation media and have proven to be quite leak resistant compared to hydraulic fluids, especially silicone fluid. Silicone elastomers have been employed due to their high thermal stability, low glass transition temperature, lack of crystallinity and high compressibility. An example of a silicone elastomer that flows like a fluid under high pressure is described in U.S. Pat. No. 3,843,601. This patent discloses the chemistry of an silicone elastomer that is easily deformed under pressure and breaks into soft particles under high shear. The particles have the property of flowing under pressure. The silicone elastomer is formed by preparing a vinyl-containing silicone fluid having a molecular weight of between 20,000 and 200,000 having predominantly dimethylsiloxane units with a small amount of methylvinyl siloxane units. The elastomer is unusual since there are between 0.074 and 0.74 free end groups on the elastomer per 100 silicon atoms. It was discovered, however, that prior art elastomers degrade under high pressure shear flow. Rendering a stable media is difficult and time consuming, for example by repeatedly shearing the media until the properties become stable. Furthermore, the material described in U.S. Pat. No. 3,843,601 would crystallize at -40.degree. C., rendering the material unsuitable for use in a landing gear shock strut application, which could operate at a temperature as low as -40.degree. C.
Therefore, a material that is more resistant to leaking than prior art hydraulic fluids is desired. More particularly, a material having the ability to flow like a fluid is desired, and that remains relatively stable when repeatedly sheared.